Tens of thousands of protesters across the US have clashed with police as tensions remained high for a sixth night after the death of unarmed black man George Floyd.

On Sunday night (local time), the protests came to within 200 metres of the White House in Washington, DC, as federal and local police, secret service agents and DEA officers in riot gear used tear gas and pepper spray to force back hundreds of demonstrators.

Crowds of men and women held signs, threw fireworks and set fire to parked cars and buildings about 10.30pm (local time). A guardhouse was reportedly set alight, along with the historic St John’s Church across Lafayette Park from the US President’s official residence.

The Washington demonstration was just one in about 40 cities across 23 American states, with National Guard troops deployed to control crowds who breached tight curfews.

On Monday (AEST), protests escalated from Boston on the east coast to San Francisco, with people rioting and looting stores in broad daylight in Philadelphia and Santa Monica, California.

So far, 4100 people have been arrested in violent confrontations with police during the past five days of demonstrations, according to The Associated Press.

At one stage on Saturday night, during the third night of the escalating demonstrations, President Donald Trump was abruptly taken to a secure bunker after hundreds of protesters gathered outside the White House, some throwing rocks and tugging at police barricades.

Mr Trump spent nearly an hour in the bunker, which was designed for use in emergencies such as terrorist attacks, according to a Republican close to the White House who spoke on condition of anonymity.

The account was confirmed by an administration official.

Across Washington, DC, 1700 National Guard soldiers were called up to support local law enforcement. National Guard troops have been deployed in 15 states in the past days.

Looters run from a convenience store during a protest at Lafayette Square Park. Photo: Getty

As night fell, protesters holding signs set fire to cars and rubbish bins. Photo: Getty

As police donned gas masks, protesters were sprayed with pepper spray and cannisters of tear gas luanched into crowds. Photo: Getty

On Monday, CNN reported “eerie scenes” of smoke-filled air as lights from flood lamps illuminated the streets around Lafayette Park, outside the White House.

Many people yelled “don’t shoot” as police pushed them out of the park onto Connecticut Avenue.

Rows of riot police stretched across the streets, as demonstrators yelled: “You are the threat”. What began as a peaceful protest during the day, during the night the violence “sky-rocketed”, CNN reported.

Less than 200 metres from the White House, hundreds of protesters confronted rioted police. Photo: AAP

Streets were largely empty by 11pm (local time) as people began to comply with curfews.

Graffiti was sprayed on buildings that read: “Why do we have to keep telling you black lives matter?”.

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Sunday night’s protests marked the latest outburst of violence following peaceful demonstrations over the death of Mr Floyd.

Mr Floyd, 46, an unarmed black man, died last Monday after a white Minneapolis police officer knelt on his neck, sparking outrage that has swept across a politically and racially divided nation.

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In one of the latest acts of violence, a tanker truck ploughed into a group of 6000 protesters marching on a closed freeway in Minneapolis. The driver was dragged from the cabin of the truck and taken into custody.

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It did not appear any marchers were struck by the tanker as it sped through the crowd on the westbound lanes of Interstate 35 on Sunday, honking. The freeway was closed to traffic at the time.

“Very disturbing actions by a truck driver on I-35W, inciting a crowd of peaceful demonstrators,” the Minneapolis Department of Public Safety said on Twitter.

Tweet from @FOX29philly

Meanwhile in Philadelphia, social media users described scenes of “total anarchy” as police cars were trashed, set ablaze and pushed into stationary vehicles. The city announced a 6pm-to-6am curfew after a day of protests and looting.

CNN reported “chaos, violence and looking” as protesters ignored curfews and ran through the city centre, looting shops and setting fires to northern parts of the city.

Sporadic violence broke out in Boston following peaceful protests as activists threw bottles at police officers and lit a vehicle on fire.

In Long Beach, California, demonstrators wearing face masks and holding up signs broke curfew about 9pm, while dozens of upscale shops in Santa Monica were looted along the city’s popular Third Street Promenade before police moved in to make arrests. The vandalism followed a largely peaceful march earlier in the beachside city.

San Francisco mayor London Breed encouraged peaceful protests across the city but urged people to stick to the 8pm to 5am curfew. After dark, hundreds of armed riot police took to the streets to quell rioters as people walked the streets setting rubbish bins on fire and setting off fireworks.

Tweet from @LondonBreed

In New York City, police arrested about 350 people and 30 officers suffered minor injuries during clashes.

Mayor Bill de Blasio said police conduct was being investigated, including widely shared videos showing a police vehicle lurching into a crowd of protesters who were pelting it with debris in Brooklyn.

Protests have also flared in Chicago, Seattle, Salt Lake City, Cleveland and Dallas.

The administration of Mr Trump, who has called protesters “thugs,” will not federalise and take control of the National Guard for now, national security adviser Robert O’Brien said on Sunday.